Speculative fix for crash in occlusion hit test for viz hit test data

If a frame is throttled, then it may have dirty layout by the time
PageAnimator::UpdateHitTestOcclusionData runs. There is no empirical
evidence that render throttling is actually causing the crashes in the
wild, so also add a diagnostic CHECK.

BUG=1035029
R=chrishtr@chromium.org

Change-Id: Ie8d1aa5d48cf94832616403e27965722b809020b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1972230Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726170}

third_party/blink/renderer/core/frame/remote_frame.cc

@@ -362,6 +362,12 @@ bool RemoteFrame::IsIgnoredForHitTest() const {
 void RemoteFrame::UpdateHitTestOcclusionData() {
   if (!cc_layer_ || !is_surface_layer_)
     return;
+  // If the parent LocalFrameView is render throttled, we may have stale layout
+  // information, so do nothing.
+  LocalFrameView* parent_view = View() ? View()->ParentFrameView() : nullptr;
+  if (!parent_view || parent_view->CanThrottleRendering())
+    return;
+  CHECK(!parent_view->NeedsLayout());
   bool unoccluded = false;
   if (base::FeatureList::IsEnabled(
           blink::features::kVizHitTestOcclusionCheck)) {